Load sensor configurations for caster assemblies of a patient support apparatus

ABSTRACT

A patient support apparatus comprises a base supported by caster assemblies with each caster assembly comprising a stem, a caster wheel, and a caster wheel axle. A patient support surface is coupled to the base and is configured to receive a load. One or more load sensors are integrated with at least one of the stem, the caster wheel, or the caster wheel axle for measuring the load. One or more of the caster assemblies can be coupled to a steering motor, which controls orientation of the caster assembly. A controller can control the steering motors based on analyzing the measurements of the load sensor. The load sensors can produce measurements indicative of both vertical load and non-vertical load applied to the caster assembly. The controller can also analyze the measurements of the load sensor to determine the load received by the patient support surface by negating the non-vertical load.

RELATED APPLICATIONS

This application is a Continuation of U.S. patent application Ser. No.16/046,150, filed on Jul. 26, 2018 and issued as U.S. Pat. No.11,123,247 on Sep. 21, 2021, which claims the benefit of and priority toU.S. Provisional Patent Application No. 62/537,659, filed on Jul. 27,2017, the entire contents and disclosures of each of which are herebyincorporated by reference in their entirety.

BACKGROUND

Patient support apparatuses such as hospital beds, stretchers, cots,wheelchairs, and chairs are routinely used by operators to move patientsfrom one location to another. Conventional patient support apparatusescomprise a base and a support surface upon which the patient rests.Wheels are coupled to the base to enable transport over floor surfaces.

Often, sensors are placed by the support surface for sensing a loadapplied to the support surface by the patient. Through the force ofgravity, a path of the load is transmitted from the support surface,through the base, and ultimately through the wheels to the floor uponwhich the patient support apparatus rests.

Having the sensors placed by the support surface has many shortcomings.For example, to achieve accurate load readings, the support surface mustbe as horizontal as possible (e.g., not tilted inlitter/fowler/gatch/trend positions) at the time of load measurement.Mainly, tilting of the support surface may cause some of the load to beapplied along load paths that circumvent the sensors. However, keepingthe support surface horizontal is not always practical because thepatient often requires movement or tilting of the support surface forconvenience or health related purposes. Physical movement of the patienton the support surface may also cause inaccurate readings when thesensors are placed by the patient support surface. Leaning or postureadjustment of the patient may similarly cause some of the load to beapplied along load paths that evade the sensors. As such, when thesensors are placed by the support surface, the sensors are placed in aposition that has potential to be bypassed, in part, by the load path.In turn, this may also inhibit the ability for accurate load readings. Apatient support apparatus with features designed to overcome one or moreof the aforementioned challenges is desired.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is perspective view of a patient support apparatus.

FIG. 2A is an elevational view, partially in phantom, of a casterassembly of the patient support apparatus according to one embodiment.

FIG. 2B is perspective view of the caster assembly of FIG. 2A.

FIG. 3 is a block diagram of one embodiment of a system of the patientsupport apparatus comprising a load sensor, a controller, and motors forcontrolling the caster assembly.

FIG. 4A is a perspective view, partially in phantom, of the casterassembly comprising the load sensor integrated around a stem of thecaster assembly, according to one example.

FIG. 4B is a cross-sectional view of the stem and load sensor of thecaster assembly of FIG. 4A wherein the stem and load sensor are at rest.

FIG. 4C is the cross-sectional view of the stem and load sensor of FIG.4B wherein the stem is undergoing an applied load detectable by the loadsensor.

FIG. 5 is a perspective view, partially in phantom, of another exampleof the load sensor integrated around the stem of the caster assembly.

FIG. 6A is a perspective view of the caster assembly comprising the loadsensor integrated on a distal end of the stem, according to one example.

FIG. 6B is a cross-sectional view of the stem and load sensor of thecaster assembly of FIG. 6A wherein a load is applied to the distal endof the stem.

FIG. 7A is a perspective view of the caster assembly comprising the loadsensor integrated on the distal end of the stem, according to anotherexample.

FIG. 7B is a cross-sectional view of the stem and load sensor of thecaster assembly of FIG. 7A wherein the stem and the load sensor are atrest.

FIG. 7C is the cross-sectional view of the stem and load sensor of FIG.7B wherein the stem is undergoing an applied load detectable by the loadsensor.

FIG. 8A is an elevational view, partially in phantom, of the casterassembly comprising the load sensor integrated on a wheel axle of thecaster assembly, according to one example.

FIG. 8B is an elevational view of the wheel axle and the load sensor ofthe caster assembly of FIG. 8A wherein the wheel axle and the loadsensor are at rest.

FIG. 8C is the elevational view of the wheel axle and the load sensor ofFIG. 8B wherein the wheel axle is undergoing an applied load detectableby the load sensor.

FIG. 9A is a perspective view, partially in phantom, of the casterassembly comprising load sensor integrated with a wheel of the casterassembly wherein the wheel is at rest.

FIG. 9B is the perspective view of the caster assembly of FIG. 9Awherein the wheel is undergoing an applied load detectable by the loadsensor.

FIG. 10A is a diagram illustrating vertical and non-vertical componentsof a load detected by the load sensor of the caster assembly, accordingto one example.

FIG. 10B is a diagram illustrating a combined vertical component of theload from FIG. 10A wherein non-vertical components of the load arenegated by the controller.

FIG. 11 is a top view of the caster assembly in a trailing positionafter being rotated from a non-trailing position by a steering motorbased on the load detected by the load sensor.

DETAILED DESCRIPTION I. Patient Support Apparatus Overview

Referring to FIG. 1 , a patient support apparatus 30 is shown for movinga patient from one location to another. The patient support apparatus 30illustrated in FIG. 1 is a hospital bed. In other embodiments, however,the patient support apparatus 30 may be a stretcher, cot, wheelchair,chair, or similar apparatus.

A support structure 32 provides support for the patient during movementof the patient support apparatus 30. The support structure 32illustrated in FIG. 1 comprises a base 34 and an intermediate frame 36.The intermediate frame 36 is spaced above the base 34. The supportstructure 32 also comprises a patient support deck 38 disposed on theintermediate frame 36. The patient support deck 38 may comprise severalsections, some of which are pivotable relative to the intermediate frame36, such as a head section, a seat section, a thigh section, and a footsection. The patient support deck 38 provides a patient support surface42 upon which the patient is supported. The patient support surface 42is supported by the base 34.

A mattress 40 is disposed on the patient support deck 38. The mattress40 comprises a direct patient support surface 43 upon which the patientis supported. The base 34, intermediate frame 36, patient support deck38, and patient support surfaces 42, 43 each have a head end and a footend corresponding to the designated placement of the patient's head andfeet on the patient support apparatus 30. The construction of thesupport structure 32 may take on any suitable design, and is not limitedto that specifically set forth above or shown in FIG. 1 .

Side rails 44, 46, 48, 50 are coupled to the intermediate frame 36. Afirst side rail 44 is positioned at a right head end of the intermediateframe 36. A second side rail 46 is positioned at a right foot end of theintermediate frame 36. A third side rail 48 is positioned at a left headend of the intermediate frame 36. A fourth side rail 50 is positioned ata left foot end of the intermediate frame 36. If the patient supportapparatus 30 is a stretcher or a cot, there may be fewer side rails. Theside rails 44, 46, 48, 50 are movable between a raised position in whichthey block ingress and egress into and out of the patient supportapparatus 30, one or more intermediate positions, and a lowered positionin which they are not an obstacle to enable such ingress and egress. Instill other configurations, the patient support apparatus 30 may notinclude any side rails.

A headboard 52 and a footboard 54 are coupled to the intermediate frame36. In other embodiments, when the headboard 52 and footboard 54 areincluded, the headboard 52 and footboard 54 may be coupled to otherlocations on the patient support apparatus 30, such as the base 34. Instill other embodiments, the patient support apparatus 30 does notinclude the headboard 52 or the footboard 54.

Operator (human control) interfaces 56, such as handles, are shownintegrated into the footboard 54 and side rails 44, 46, 48, 50 tofacilitate movement of the patient support apparatus 30 over the floorsurfaces. Additional operator interfaces 56 may be integrated into theheadboard 52 and/or other components of the patient support apparatus30. The operator interfaces 56 are graspable by the operator tomanipulate the patient support apparatus 30 for movement. The operatorinterface 56 may comprise one or more handles coupled to theintermediate frame 36. The operator interface 56 may simply be a surfaceon the patient support apparatus 30 upon which the operator locallyapplies force to cause movement of the patient support apparatus 30 inone or more directions, also referred to as a push location. This maycomprise one or more surfaces on the intermediate frame 36 or base 34.This could also comprise one or more surfaces on or adjacent to theheadboard 52, footboard 54, and/or side rails 44, 46, 48, 50. In otherembodiments, the operator interface 56 may comprise separate handles foreach hand of the operator. For example, the operator interface 56 maycomprise two handles. Other forms of the operator interface 56 are alsocontemplated.

One or more caster assemblies 58 are coupled to the base 34 tofacilitate transport over floor surfaces. In one example, as shown inFIG. 1 , four caster assemblies 58 a-58 d are arranged in each of fourquadrants of the base 34 adjacent to corners of the base 34. In theembodiment shown, the caster assemblies 58 a-58 d are able to rotate andswivel relative to the support structure 32 during transport.

The caster assemblies 58 may be non-steerable, steerable, non-powered,powered (driven), or any combinations thereof. The caster assemblies 58may have any suitable shape or configuration other than those shown inthe Figures.

The patient support apparatus 30 may comprise any suitable number ofcaster assemblies 58, such as two or six, etc. The caster assemblies 58may have any suitable configuration and arrangement depending on thespecific type of patient support apparatus 30. For example, when thepatient support apparatus 30 is a wheelchair, the patient supportapparatus 30 may comprise two front non-driven caster assemblies 58 andtwo rear driven caster assemblies 58.

As shown in FIGS. 2A and 2B, each caster assembly 58 comprises a stem60, a caster wheel 62, and a caster wheel axle 64. The caster wheel 62rotates about a rotational axis R of the wheel axle 64 to effect motionof the patient support apparatus 30, such as along a floor surface. Thecaster wheel 62 has a radial center 63. The caster wheel 62 may be anairless (non-pneumatic) wheel or may be an inflatable, pneumatic orsemi-pneumatic wheel. The stem 60 extends from the caster assembly 58 toprovide an interface connection to the base 34, as shown in one exampleof FIG. 2B. The stem 60 may be any suitable shape, such as cylindrical,box shaped, or the like. The caster assembly 58, and more specifically,the stem 60 may be coupled to the base 34 according to any suitablemanner and using any suitable fastening mechanism.

The caster wheel 62 rotates vertically about a swivel axis S definedthrough the stem 60. The stem 60 and swivel axis S may be offset withrespect to the radial center 63 of the caster wheel 62, as shown in FIG.2B. In other words, the swivel axis S and the rotational axis R do notdirectly intersect. In such instances, the caster wheel 62 exhibits atrailing orientation, meaning a bulk, offset portion, of the casterwheel 62 trails behind the swivel axis S when the caster wheel 62 is inmotion. In another example, the swivel axis S is aligned with the radialcenter 63 and intersects the rotational axis R of the caster wheel 62.In such instances, the caster wheel 62 has no specific trailingorientation and either side of the caster wheel 62 may trail behind theswivel axis when the caster wheel 62 is in motion.

Caster assemblies 58 and structures, functions and applications thereofmay be like those described in U.S. Patent Application Publication No.2016/0089283, entitled “Patient Support Apparatus,” the disclosure ofwhich is hereby incorporated by reference in its entirety.

Additionally, one or more auxiliary wheels 66 (powered or non-powered),which may be movable between stowed positions and deployed positions,may be coupled to the support structure 32. In some cases, when theseauxiliary wheels 66 are located between the caster assemblies 58 andcontact the floor surface in the deployed position, they cause two ofthe caster assemblies 58 to be lifted off the floor surface therebyshortening a wheel base of the patient support apparatus 30. Suchauxiliary wheels 66 may also be arranged substantially in a center ofthe base 34.

The patient support apparatus 30 comprises a controller 68 incommunication with and for controlling any suitable components of thepatient support apparatus 30, such as the electrical orelectromechanical components described herein. The controller 68 maycomprise any suitable signal processing means, computer executableinstructions or software modules stored in non-transitory memory whereinthe executable instructions or modules may be executed by a processor,or the like. Additionally, or alternatively, the controller 68 maycomprise a microcontroller, a processor, one or more integratedcircuits, logic parts, and the like for enabling the same. Thecontroller 68 may have any suitable configuration for enablingperformance of various tasks related to operation of the patient supportapparatus 30, such as those described below. The controller 68 may belocated at any suitable location of the patient support apparatus 30.

As shown in FIG. 1 , the patient support apparatus 30 may comprise oneor more steering motors 70 a-70 d for changing an orientation of thecaster assemblies 58 about the swivel axis S. The steering motor 70 maybe coupled to the stem 60 of the caster assembly 58. Each steering motor70 may change the orientation of the caster assemblies 58 to facilitatesteering of the patient support apparatus 30. For example, the steeringmotors 70 may change orientation of the caster assemblies 58 help tomove patient support apparatus 30 in the direction desired by thecaregiver. One steering motor 70 may be associated with each casterassembly 58, and more specifically, the stem 60 of the caster assembly58. Alternatively, the steering motors 70 may be associated with onlycertain caster assemblies 58, e.g., the front-leading caster assemblies58 a, 58 b. The steering motors 70 may be located inside or outside therespective caster assembly 58.

Referring to FIG. 3 , the steering motors 70 are coupled to thecontroller 68. The steering motors 70 may be directly wired to thecontroller 68 or in wireless communication with the controller 68. Thesteering motors 70 may receive control signals from the controller 68commanding reorientation of the respective caster assemblies 58. Forexample, the control signals may be derived from the controller 68receiving readings indicative of user applied force and direction offorce when pushing patient support apparatus 30. Additional examples ofcontrol signals provided by the controller 68 to effect reorientation bythe steering motors 70 are described below. Steering motors 70 andtechniques for generating signals for controlling the same may be likethose described in U.S. Patent Application Publication No. 2016/0089283,entitled “Patient Support Apparatus,” the disclosure of which is herebyincorporated by reference in its entirety.

In embodiments where one or more caster assemblies 58 are driven, adrive motor 72 a-72 d may be associated with the respective casterassembly 58, as shown in FIG. 1 . The drive motor 72 is configured tocause the caster assembly 58 to rotate about the rotational axis R ofthe caster assembly 58. The drive motor 72 may be coupled to the casterwheel axle 64. Referring to FIG. 3 , the drive motors 72 are coupled tothe controller 68. The drive motors 72 may be directly wired to thecontroller 68 or in wireless communication with the controller 68. Thedrive motor 72 is configured to cause the caster assembly 58 to rotatein response to receiving control signals provided by the controller 68.For example, the controller 68 may command the drive motor 72 to rotatethe respective caster assembly 58 to effect a desired velocity for thepatient support apparatus 30 based on user input and/or sensed readingsrelating to the environment of the patient support apparatus 30. Thedrive motor 72 may be located inside of the respective caster assembly58. Drive motors 72 and techniques for generating signals forcontrolling the same may be like those described in U.S. PatentApplication Publication No. 2016/0089283, entitled “Patient SupportApparatus,” the disclosure of which is hereby incorporated by referencein its entirety.

II. Load Sensor Configurations For Caster Assemblies

Referring to FIGS. 3-9 , the patient support apparatus 30 comprises oneor more load sensors 80 that are utilized for measuring a load appliedto the patient support apparatus 30. For instance, the load is appliedto one or more of the patient support surfaces 42, 43. The load may beapplied from any object, such as a patient, placed on one or more of thepatient support surfaces 42, 43. The load is not applied when the objectis removed or otherwise not placed on one or more of the patient supportsurfaces 42, 43. Specific structural embodiments and locations of loadsensors 80 in relation to the patient support apparatus 30 are describedbelow.

More specifically, the load sensor 80 is integrated into and/or with thecaster assembly 58, or components thereof. That is, the load sensor 80is integrated with the caster assembly 58 during manufacturing/assemblyof the caster assembly 58. In other words, by being integrated with thecaster assembly 58, the load sensor 80 is not disposed on a componentthat is separate from the caster assembly 58 or a component that isotherwise not involved with functionality of the caster assembly 58.Instead, the load sensor 80 is “in-line” with the caster assembly 58thereby eliminating a need for secondary support structures, such ascantilevers, separately attached to the caster assembly 58 forexperiencing the load and holding the load sensor 80. Installation ofthe caster assembly 58 having the integrated load sensor 80 is madeseamlessly to the base 34 without including additional features coupledto the base 34 and/or caster wheel 58 for accommodating such secondarysupport structures for the load sensor 80.

As will be shown in the various examples below, the load sensor 80 iscooperative with at least one of the stem 60, the caster wheel 62, andthe caster wheel axle 64 of the caster assembly 58 to measure the load.One or more load sensors 80 are affixed, attached, or otherwise directlycoupled to the stem 60, the caster wheel 62, and/or the caster wheelaxle 64, individually, or in combination. In other examples, the loadsensor 80 is coupled to the steering motor 70 and/or the drive motor 72,when such motors 70, 72 are integrated with the caster assembly 58.

Furthermore, by having the load sensor 80 integrated with the casterassembly 58, there is an opportunity to avoid placing load sensors 80 bythe patient support surfaces 42, 43. Mainly, the path of the loadtransmitted from the patient support surfaces 42, 43 will ultimatelybottle-neck and pass through the caster assemblies 58 to the floor uponwhich the patient support apparatus 30 rests. Therefore, having the loadsensors 80 integrated with the caster assemblies 58 provides a uniqueopportunity to accurately and completely capture the applied load.Because the caster assemblies 58 are usually placed on a horizontal andstable floor surface, load sensors 80 will also be in a horizontal statethereby providing accurate readings. Thus, the described configurationavoids the shortcomings of having the support surfaces 42, 43 be ashorizontal as possible (e.g., not tilted) at the time of loadmeasurement to provide accurate readings. Even if the support surfaces42, 43 are tilted in litter/fowler/gatch/trend positions, the load pathmust find its way through the caster assembly 58 such that circumventionof the load sensors 80 by the load path is unlikely. Thus, integratingthe load sensor 80 with the caster assembly 58 will provide free tiltingof the support surfaces 42, 43 for convenience or health relatedpurposes of the patient, even during load measurement.

The described configuration further provides accurate readings even withphysical movement of the patient on the support surfaces 42, 43 duringload measurement. Leaning or posture adjustment of the patient isunlikely to cause some of the load to be applied along load paths thatevade the load sensor 80 because the load sensor 80 is provided at thecaster assembly 58 near the floor, and at a low and bottle-necked pointin the load path. Additional advantages of the load sensor 80configurations will be appreciated from the examples described below andthose shown in the figures.

Of course, there may be other load sensors disposed in locations of thepatient support apparatus 30 other than being integrated on or withinthe caster assembly 58. These other load sensors may be utilized inconjunction with or separately from any load sensor 80 integrated withthe caster assembly 58.

As used herein, the term “load sensor” is not limited to a sensor onlyconfigured to measure the load directly. Since the load may be difficultto characterize based on sensor readings alone, and because varioustypes of load sensors 80 are provided herein, it should be understoodthat load sensor 80 may produce readings that are indicative of, orcorresponding to, the load such that the load can be inferred based onsuch readings. Examples of such readings are understood from the variousexamples of the load sensor 80, as described below.

The load sensor 80 integrated with the caster assembly 58 may have anysuitable configuration for sensing the load. For example, the loadsensor 80 may be any type of load cell, such as a strain gauge loadcell, a piezoelectric load cell, a hydraulic load cell, a pneumatic loadcell, or the like. The load cell may be bending beam, compression,push-pull rod type or the like. The load cell may measure forces/torquesapplied by the load in any number of degrees of freedom, such as sixdegrees of freedom, as shown in FIG. 5 , including forces along axes X,Y, Z and torques (pitch, roll, yaw) about these axes, respectively. Theload cell may have configurations other than those described herein.

The load sensor 80 integrated with the caster assembly 58 may alsocomprise one or more strain gauges for converting strain caused by theapplied load into signals. The strain gauges may be any suitable type,such as foil type, piezoresistive type, semiconductor based,microelectromechanical system (MEMS) type, or the like. The straingauges may have configurations other than those described herein.

In other examples, the load sensor 80 integrated with the casterassembly 58 is a pressure sensor for converting pressure caused from theapplied load into signals. The pressure sensor may use any suitabletechnology, such as piezoresistive, capacitive, electromagnetic,piezoelectric, and the like. The sensed pressure may be applied to anysuitable medium, such as pressure applied to liquid, solid or gases. Thepressure sensor may have configurations other than those describedherein.

The load sensor 80 integrated with the caster assembly 58 may be adisplacement sensor for converting physical displacement of an objectinto signals. The displacement sensor may have various configurations,such as a linear, rotational, inductive, capacitive, electrical, encoderbased, potentiometric, optical sensors, or the like. The displacementsensor may have configurations other than those described herein.

Any of the examples for the load sensor 80 may be utilized individually,or in combination for any one or more load sensors 80. Any other type ofload sensor 80 other than those described herein may be utilized.

As shown in FIG. 3 , the load sensors 80 are coupled to the controller68 and provide readings or measurements to the controller 68. The loadsensors 80 may be directly wired to the controller 68 or in wirelesscommunication with the controller 68. When wired, electrical circuitsmay be passed from the caster assembly 58, through the base 34, and tothe controller 68. In wireless configurations, the load sensor 80 may beoutfitted with an integrated antenna (e.g., printed circuit board (PCB)antenna) and may communicate using any suitable communication protocolor standard, such as Bluetooth, Zigbee, ISA100.11a, WirelessHART, MiWi,WiFi, near field communication (NFC), or the like. The load sensor 80and the controller 68 may be coupled according to any suitable networkscheme, such as local area network (LAN), body area network (BAN),personal area network (PAN), wireless PAN (WPAN), low-rate WPAN(LR-WPAN), wide area network (WAN), or the like. Communication may occurat any suitable frequency band. The load sensor 80 may also beintegrated on a PCB within a larger component, such as a module, whichincludes additional functionality, such as communication capabilities asdescribed in any of the examples described herein.

The readings of the load sensor 80 may be of different types (e.g.,analog, digital, etc.) depending on the configuration of the loadsensors 80. The controller 68 may comprise a load analyzer 82 embodiedas hardware and/or software for analyzing the readings from the loadsensors 80. The load analyzer 82 may also reference a transformation orcalibration matrix that is storable in memory of the controller 68. Thematrix transforms the raw measurement values from the load sensor 80into the resulting forces and torques.

The load analyzer 82 may analyze the load readings for making one ormore determinations. For instance, the controller 68 may be coupled to auser interface 84, which is configured to receive user input commandsand to display information to the user. The load sensors 80 may beutilized as part of a scale system. The load analyzer 82 may determine aweight of the patient based on the readings from the load sensors 80.The determined patient weight may be displayed on the user interface 84.Thus, the load sensors 80 may be understood as weight sensors in certainexamples. In other examples, the controller 68 may make determinationsfor commanding the steering motor 70 and/or drive motor 72 based on anoutcome of analyzing the load sensor 80 readings. Examples of motorcontrol based on load sensor 80 readings are provided below.

As shown in the examples of FIGS. 4-7 , the load sensor 80 is coupled tothe stem 60. Here, the load sensor 80 is configured to measure loadapplied to the stem 60.

In one example, as shown in FIGS. 4 and 5 , the load sensor 80 isdisposed about or around the stem 60. Because the stem 60 has acylindrical configuration in FIG. 4A, the load sensor 80 is disposedannularly or circumferentially about the stem 60. Of course, where thestem 60 has other cross-sectional configurations (e.g., rectangular,etc.), the load sensor 80 may be disposed around any number of edges orfaces of the stem 60. The load sensor 80 may entirely surround a portionof the stem 60 (as shown in FIG. 4A). Alternatively, the load sensor 80may partially surround a portion of the stem 60.

In the embodiment shown in FIGS. 4A-4C, the load sensor 80 is embodiedas a load cell. Of course, the load sensor 80 may have otherconfigurations besides or in addition to a load cell in this example.FIG. 4B shows a cross-sectional view of the load sensor 80 and stem 60of FIG. 4A at rest. FIG. 4C shows a cross-sectional view of the loadsensor 80 and stem 60 of FIG. 4A under load. In this example, the loadsensor 80 has a disc-shape, but the load sensor 80 may have othershapes. The load sensor 80 is, or has, a deformable member coupledbetween a first side 82 that is fixed and an opposing second side 84that moves. The first side 82 is fixed to a rigid structure of thecaster assembly 58, such as a housing component (not shown). The secondside 84 is coupled to at an inner side to the stem 60 and movesaccording to movement of the stem 60. The load sensor 80 may compriseany suitable number of strain gauges integrated therewith for sensingstrain from the deformation.

The load sensor 80 is configured to undergo compression in response tothe load applied to the stem 60 or tension in response to removal of theload. The stem 60 may shift according to any one of six degree offreedoms. In one example, as shown in FIG. 4C, the stem 60 slightlyshifts downward due to vertical downward force and shifts at an angledue to non-vertical forces. The resulting circumferential deformation ofthe surrounding load sensor 80 caused by shifting of the stem 60 issensed for measuring these vertical and non-vertical forces, if present.The shifting of the stem 60 and deformation of the load sensor 80 inFIG. 4C are exaggerated for illustrative purposes and may not berepresentative of actual conditions, which may not be directlynoticeable to the naked eye. Furthermore, the load sensor 80 may haveany suitable thickness other than the thickness shown in FIG. 4C.

In this example, the load sensor 80 configuration can take into accountthe rotational moment force caused by the offset in caster assembly 58.That is, in situations where the caster assembly 58 is offset, the loadapplied will tend to pass to the floor through a path that is notdirectly through the swivel axis S. Instead, load path will pass throughthe radial center 63 of the caster wheel 62, which is offset from theswivel axis S, as described. Therefore, the load path may take an abruptdeviation from the swivel axis S, thereby causing non-vertical forcesthat tilt the stem 60, as shown in FIG. 4C. Described below aretechniques for compensating for these non-vertical forces.

FIG. 5 shows another example of the load sensor 80 disposed about oraround the stem 60. Again, the first side 82 is fixed to a rigidstructure of the caster assembly 58 and the second side 84 is coupled toat an inner side to the stem 60. Here, a plurality of spokes 86 connectthe fixed and moveable sides 82, 84. The spokes 86 bend in response toapplication of the load to stem 60. The load sensor 80 in FIG. 5 hasfour spokes 86, however, any number of spokes 86 may be utilized. Aplurality of strain gauges 88 attach to each spoke 86 for measuring thestrain on the spoke 86. Each spoke 86 and the strain gauges 88associated with each spoke 86 collectively form a single-axis load cellin load sensor 80. The spokes 86 bend in response to load applied to thestem 60. As shown in FIG. 5 , the strain gauges 88 attach to the top,bottom, and sides of each spoke 86 for measuring strain on the spokes 86resulting axial loads along the X, Y, and/or Z-axes, and/or rotationalloads about the X, Y, and/or Z-axes. As such, the load sensor 80 in FIG.5 is configured to measure the applied load in six-degree of freedom.The load sensor 80 may be disposed about or around the stem 60 accordingto configurations other than those shown in FIGS. 4 and 5 .

Referring now to FIGS. 6 and 7 , another example is shown wherein theload sensor 80 is disposed on a distal end 90 of the stem 60. In thisexample, the load sensor 80 has the first side 82 fixed to a rigidstructure (not shown) of the caster assembly 58 or base 34 and thesecond side 84 coupled to the distal end 90 of the stem 60. In thisexample, either the first side 82 or the second side 84 of the loadsensor 80 may be coupled to a non-moving member. That is, the stem 60 inthis example may be stationary or non-moving, and the rigid structure ofthe caster assembly 58 or base 34 may move based on the applied load, orvice-versa.

In the example of FIGS. 6A and 6B, the load sensor 80 is a load cellconfigured to measure compressional force applied to the distal end 90of the stem 60, or absence thereof. Because the stem 60 has acylindrical configuration in FIG. 6 , the load sensor 80 also has acylindrical configuration. Of course, where the stem 60 has othercross-sectional configurations (e.g., rectangular, etc.), the loadsensor 80 may have similar cross-sectional configurations.Alternatively, the load sensor 80 may have a cross-sectionalconfiguration that differs from the cross-sectional configuration of thestem 60. The load sensor 80 may entirely occupy a surface area of thedistal end 90 of the stem 60 (as shown in FIG. 6 ). Alternatively, theload sensor 80 may occupy a portion of the surface area of the distalend 90. The load sensor 80 may be coupled to the distal end 90 accordingto any means that preserves accurate load measurement, such asmechanical mounting, adhesive, welding, or the like.

FIG. 6B shows a cross-sectional view of the load sensor 80 and stem 60of FIG. 6A under load. The load sensor 80 is, or has, a compressivemedium coupled between the first and second sides 82, 84. Thecompressive medium may be a solid, liquid or gas. The load sensor 80 maybe hermetically sealed to be airtight from the environment. The loadsensor 80 may have a low-profile to not interfere with installation orconnection of the caster assembly 58 to the base 34. The load sensor 80may have any suitable thickness other than the thickness shown in FIG.6B. The load sensor 80 is configured to undergo compression in responseto the load applied to the distal end 90. In one example, as shown inFIG. 6B, the load sensor 80 compresses (not shown) due to verticaldownward force. The resulting compression of the load sensor 80 issensed for measuring these vertical downward forces, if present.Compression of the load sensor 80 in FIG. 6B may not be directlynoticeable to the naked eye. In this example, the compression loadsensor 80 may similarly take into account the rotational moment forcecaused by the offset in caster assembly 58, as described above.

FIGS. 7A-7C illustrate another example of the load sensor 80 beingdisposed on the distal end 90 of the stem 60. In this example, the loadsensor 80 is a displacement sensor configured to undergo displacement inresponse to the load applied to the distal end 90 of the stem 60. Theload sensor 80 measures the resulting displacement, which is indicativeof the applied load. The controller 68 can convert displacement readingsinto force readings using the load analyzer 82 and any suitabletransformation matrix. In FIG. 7A-7C, the displacement sensor isembodied with a biasing member 92, such a coil spring. Other biasingmembers 92 other than a coil spring may be utilized, such as tension(torsion) spring, leaf (flat) spring, conical springs, wire ringsprings, or the like. The biasing member 92 may have any appropriatespring constant, which can be calibrated for expected loads applied tothe patient support apparatus 30. In this example, the load sensor 80has a cylindrical shape, but the load sensor 80 may have other shapes,as described.

In this example, the load sensor 80 has the first side 82 fixed to arigid structure of the caster assembly 58 or base 34 and the second side84 coupled to the distal end 90 of the stem 60. In this example, eitherthe first side 82 or the second side 84 of the load sensor 80 may becoupled to a non-moving member. That is, the stem 60 in this example maybe stationary or non-moving, and the rigid structure of the casterassembly 58 or base 34 may move based on the applied load, orvice-versa. Specifically, in FIG. 7 , the first side 82 of the biasingmember 92 is coupled to a plate 94 that is in-line with the distal end90. A plunger 96 is coupled between the plate 94 and the distal end 90of the stem 60. The load sensor 80 may comprise any suitable sensor,such as those described above, for measuring displacement of the biasingmember 92, plate 94 and/or plunger 95.

FIG. 7B shows a cross-sectional view of the load sensor 80 and stem 60of FIG. 7A at rest. FIG. 7C shows a cross-sectional view of the loadsensor 80 and stem 60 of FIG. 7A under load. At rest, the biasing member92 has a length L, as shown in FIG. 7B. Under load, the biasing member92 has a different length, L′, which will vary depending on themagnitude of the load. The biasing member 92 compresses when a verticaldownward force is applied to the distal end 90. Such compression may bedue to force applied downward from movement of the plate 94 and/or fromupward force applied from movement of the stem 60. The length L′ of thebiasing member 92 decreases as compared with the length L in the at-reststate as a result of this compression. The resulting displacement isshown by Δ in FIG. 7C, which is a difference between L and L′. In FIG. 7, the displacement is measured in the Z-direction. However, it should beappreciated that the displacement may be according to any otherdirection or directions depending on the configuration of the biasingmember 92. For example, displacement may be measured in a rotationalfashion, e.g., by measuring how much the biasing member 92 has twistedbased on the load, or the like.

In some examples, more than one load sensor 80 may be stacked on top ofone another over the distal end 90 of the stem 60. These stacked loadsensors 80 may be of a similar or a different configuration from oneanother. Furthermore, load sensors 80 coupled directly to the distal end90 of the stem 60 may have configurations other than those shown inFIGS. 6 and 7 and may measure load according to techniques other thanthose shown.

Referring now to FIG. 8 , another example is illustrated wherein theload sensor 80 is coupled to the caster wheel axle 64 and is configuredto measure load applied to the caster wheel axle 64. The caster wheelaxle 64 comprises a first end 100 and a second end 102, which arecoupled to the caster wheel 62. These ends 100, 102 may be fastened tothe caster wheel 62 using any suitable means, such as bolts as shown inFIG. 8 , or the like.

The load sensor 80 may be disposed according to any suitable fashion incooperation with the caster wheel axle 64, or any part thereof. Forexample, as shown in FIG. 8 , the load sensor 80 is disposed on asurface of the caster wheel axle 64 and along the rotational axis R ofthe caster wheel axle 64. The load sensor 80 may have any suitablelength along the caster wheel axle 64. For example, the load sensor 80may extend along an entirety or a portion of the length of the casterwheel axle 64. More than one load sensor 80 may extend along therotational axis R of the caster wheel axle 64 and such load sensors 80may be disposed circumferentially on opposing faces of the caster wheelaxle 64, e.g., four load sensors 80 being 90 degrees apart from oneanother.

Additionally or alternatively, one or more load sensors 80 may bedisposed annularly or circumferentially about the caster wheel axle 64and the rotational axis R. One or more load sensors 80 may entirelysurround a portion of the caster wheel axle 64 or may partially surrounda portion of the caster wheel axle 64. Such load sensors 80 may bedisposed laterally on opposing sides of the caster wheel axle 64, e.g.,every 1 mm along the length of the caster wheel axle 64.

Additionally or alternatively, one or more load sensors 80 may becoupled to each of the ends 100, 102 of the caster wheel axle 64 forsensing the load. In such scenarios, the load sensors 80 may measure asheer force applied between the caster wheel axle 64 and the ends 100,102 of the caster wheel axle 64.

In the embodiment shown in FIGS. 8A-8C, the load sensor 80 is embodiedas a load cell. The load sensor 80 may comprise any suitable number ofstrain gauges integrated with the caster wheel axle 64 for sensingstrain from the application of the load to the caster wheel axle 64. Ofcourse, the load sensor 80 integrated with the caster wheel axle 64 mayhave any other configuration besides or in addition to a load cell, suchas those described above.

FIG. 8B shows an isolated view of the load sensor 80 and caster wheelaxle 64 of FIG. 8A at rest. FIG. 8C shows the load sensor 80 and casterwheel axle 64 of FIG. 8A under load. The load sensor 80 is configured toundergo compression or tension, depending on its positioning, inresponse to the load applied to the caster wheel axle 64 or in responseto removal of the load. The caster wheel axle 64 may bend or deformalong according to any one of six degree of freedoms. In one example, asshown in FIG. 8C, the caster wheel axle 64 slightly bends downward dueto vertical downward force from the load. The resulting deformation ofthe caster wheel axle 64 is sensed by the load sensor 80 for measuringthis vertical force, if present. The bending of the caster wheel axle 64and the load sensor 80 in FIG. 8C are exaggerated for illustrativepurposes and may not be representative of actual conditions, which maynot be directly noticeable to the naked eye.

As with the above examples, the load sensor 80 configuration in FIG. 8is also equipped to take into account the rotational moment force causedby the offset in caster assembly 58. As described, the load path withthe offset caster assembly 58 will pass through the radial center 63and/or rotational axis R of the caster wheel 62. Therefore, sensing theload on the caster wheel axle 64 is particularly suitable for accountingfor rotational moment force caused by the offset because the casterwheel axle 64 is directly in the offset load path. The load sensors 80may be cooperative with the caster wheel axle 64 for sensing the loadaccording to configurations other than those described herein.

In another embodiment, the load sensor 80 may be integrated with thecaster wheel 62. In such examples, the load sensor 80 is configured tomeasure load applied to caster wheel 62. The load sensor 80 may beintegrated with the caster wheel 62 according to various manners. Forinstance, the load sensor 80 may be integrated with any one or more ofan interior surface of the caster wheel 62, an exterior surface of thecaster wheel 62, an interior volume 110 of the caster wheel 62, and/orany other component of the caster wheel 62, such as a wheel rim, wheeltread, wheel disc, wheel bearing, wheel fastener, wheel valve stem,wheel belt, wheel braking or steering member, or the like. Any number ofload sensors 80 may be integrated with the caster wheel 62.

In one example, as shown in FIG. 9 , the caster wheel 62 is aninflatable type and comprises pressurized air within the interior volume110 of the caster wheel 62. In FIG. 9 , the pressurized air is shownonly for a portion of the interior volume 110 for simplicity. In thisexample, the load sensor 80 is embodied as a pressure sensor configuredto measure air pressure of the caster wheel 62. The load sensor 80 maybe disposed at any suitable location for measuring air pressure. Asshown in FIG. 9 , the load sensor 80 is disposed in the interior volume110 of the caster wheel 62. For example, the load sensor 80 is coupledto a surface of the caster wheel 62 that defines the interior volume110, such as the wheel rim. The load sensor 80 may be integrateddirectly at the wheel valve stem of the caster wheel 62 or integrated ona flexible band coupled to the wheel rim. However, as described, otherlocations for the load sensor 80 are contemplated. In this example, theload sensor 80 wirelessly transmits readings to the controller 68 usingany of the techniques described herein, or the like.

FIG. 9A shows the load sensor 80 measuring air pressure of the casterwheel 62 when the caster wheel 62 is at rest, e.g., without load beingapplied. FIG. 9B shows the load sensor 80 measuring air pressure of thecaster wheel 62 when load is applied to the caster wheel 62. The appliedload causes compression of the interior volume 110 of the inflatablecaster wheel 62 relative to the floor surface, as shown in FIG. 9B. As aresult, the pressure of the air within the interior volume 110increases. This increase in air pressure is indicative of the appliedload and is detected by the load sensor 80. The controller 68 canconvert pressure readings into force readings using the load analyzer 82and any suitable transformation matrix. The load sensor 80 may measureair pressure according to other techniques not described herein.

In other examples for measuring air pressure, the load sensor 80 maymeasure physical characteristics of the caster wheel 62 such that thecontroller 68 and load analyzer 82 can implement algorithms (such asspectrum analysis) to predict the air pressure. Such physicalcharacteristics may comprise angular velocity of the caster wheel 62,frequencies emitted by the caster wheel 62 during rotation, and thelike.

The caster wheel 62 may be an airless (non-inflatable) wheel, whereinthe interior volume 110 is occupied by solid material, such ascompressible rubber, polymer, etc. In such examples, air pressure isnon-existent, and the load sensor 80 instead may be embodied as a loadcell or strain gauge integrated on and/or within the solid material. Asthe solid material of the caster wheel 62 compresses under the appliedload, the load sensor 80 is able to the detect strain indicative of theload. The load sensor 80 may be integrated with the caster wheel 62according to techniques other than those described herein.

As with the above examples, the load sensor 80 configuration in FIG. 9is also equipped to take into account the rotational moment caused bythe offset in caster assembly 58. As described, the load path with theoffset caster assembly 58 will pass through the radial center 63 and/orrotational axis R of the caster wheel 62. Therefore, sensing the load onthe caster wheel 62 is particular suitable for accounting for rotationalmoment caused by the offset because the caster wheel 62 is directly inthe offset load path.

Referring now to FIGS. 10 and 11 , techniques are described foranalyzing readings of the load sensor 80 with the controller 68 andexecuting control schemes based on analysis of the load sensor 80readings.

As described, the load sensor 80, in many embodiments, is configured tomeasure the load according to many degrees of freedom. In other words,the applied load may have various components of force and/or torque. Forinstance, as described throughout, the load on the caster wheel 62 maycomprise rotational moment caused by the offset nature of the casterwheel 62. Thus, the components of force and/or torque may have magnitudeand direction. The direction of the load components may depend on manyfactors, such as the load path, the configuration and/or location of theload sensor 80 on the caster assembly 58, the nature of the appliedload, and the like.

Because the load sensor 80 is particularly configured for the patientsupport apparatus 30, accurately measuring the weight of the patientbased on the sensed load is important. In order to accurately measurethe patient weight, the primary focus of the applied load is a verticalcomponent of the load, e.g., load in the downward Z-axis direction. Forexample, the vertical component of the load may be understood as theload component directed from the patient support surfaces 42, 43 to thefloor surface. However, the load sensor 80 may produce measurementsindicative of vertical load and non-vertical load applied to the casterassembly 58, as described above. These non-vertical components may berotational moments and/or forces in non-vertical directions, such as inthe X or Y-axis directions.

Upon receiving the load measurements from the load sensor 80, thecontroller 68, and load analyzer 82, may be configured to analyze themeasurements to decompose these vertical and non-vertical components ofthe load. The controller 68 is configured to utilizecomputer-implemented techniques for negating the non-vertical componentsof the load. As a result, the controller 68 can output loaddeterminations based on the vertical component of the load. Thecontroller 68 may use software for implementing these techniques and mayinclude known geometric data, such as calibration data, about the casterassembly 58 or any component thereof, and about the load sensor 80 foranalyzing the load.

To illustrate according to one simplified example, FIG. 10A is a diagramillustrating vertical and non-vertical components of the load applied toa rigid body as detected by the load sensor 80. As illustrated, thecontroller 68 decomposes the load into four separate vectors, i.e., a,b, c, d. In this example, the vectors each have a vertical componenta_(z), b_(z), c_(z), d_(z), which is a Z-axis downward force, and anon-vertical component, a_(x), b_(x), c_(x), d_(x), which in thisexample is an X-axis horizontal force. Here, vector a is purelyhorizontal and therefore has a vertical component a_(z) equal to zero.Vector c is purely vertical and therefore has a non-vertical componentc_(x) equal to zero. Vectors b and d have non-zero vertical andnon-vertical components. Of course, illustration of these loadcomponents in FIG. 10 is for illustrative purposes and the controller 68may decompose the load with or without any such visualization.

FIG. 10B is a diagram illustrating a combined vertical component of theload from FIG. 10A wherein non-vertical components of the load arenegated by the controller 68. Here, the controller 68 negates, orotherwise factors out the non-vertical components a_(x), b_(x), c_(x),d_(x) decomposed from the applied load and preserves the verticalcomponents a_(z), b_(z), c_(z), d_(z). Specifically, the controller 68generates a vector n having a vertical component n_(z) having amagnitude based on the combination of the magnitudes of the verticalcomponents a_(z), b_(z), c_(z), d_(z). In turn, the controller 68 canuse computer-implemented techniques to extract the vertical componentfrom the applied load quickly and accurately.

The phrases “vertical” and “non-vertical” with respect to the load, orcomponents thereof, are orientation specific, i.e., Z-axis direction andnon-Z-axis direction, respectively. However, it is fully contemplatedthat the controller 68 can negate any component of the load depending onthe component of the load desired for extraction. For instance, thecontroller 68 may alternatively negate the vertical load whereextraction of the horizontal load is desired. Furthermore, the examplein FIG. 10 shows vector components only for forces along the Z andX-axes. As described, the load may comprise rotational moments about anyof the axes and therefore, the controller 68 may extract and/or negateany rotational moments. The controller 68 may do so using advancedvector analysis or any other mathematical technique.

Referring to FIG. 11 , one example of control executed by the controller68 in response to analysis of the load sensor 80 readings is described.In this example, the caster assembly 58 is an offset-type and thereforehas a trailing orientation. The load sensor 80 is integrated with thecaster assembly 58 according to any technique described herein. Thecontroller 68 analyzes the load sensor 80 readings to determine a stateof the caster assembly 58. Specifically, the controller 68 can determinea location and/or orientation of the caster assembly 58 based on theload readings. For example, using techniques wherein the load sensor 80is disposed around the stem 60 such as shown in FIGS. 4 and 5 , the loadsensor 80 detects circumferential strain relative to the stem 60. Usingthis detection alone, or in conjunction with stored calibration data,the controller 68 can determine that the caster wheel 62 is in aspecific orientation.

For instance, as shown in FIG. 11 , the offset caster assembly 58 isshown in a top view in a first state (shown in phantom). Because of theoffset configuration, the load sensor 80 detects a rotational moment.The rotational moment is detected about an axis that is parallel toposition of the rotational axis R of the caster wheel 62. In the firststate as shown in FIG. 11 , the rotational axis R of the caster wheel 62extends vertically (from the top view), and hence, the rotational momentwould be about an axis that extends vertically across the swivel axis S.From this, the controller 68 can determine the orientation of therotational axis R, and ultimately, the orientation of the caster wheel62, which in this example is trailing to the left. Using this technique,the controller 68 can determine the orientation of the caster wheel 62in full range of motion, e.g., 360 degrees about the swivel axis S.

The weight and bulk of the patient support apparatus 30, including theweight of the patient supported thereon, can make it difficult for acaregiver to manually wheel the patient support apparatus 30 from onelocation to another. Free rotational movement of the caster assemblies58 can increase this difficulty. Mainly, much of the effort ininitiating movement of the patient support apparatus 30, such as bypushing or pulling on the headboard 52, is directed to first causingcaster assemblies 58 to align with the direction of desired movement(shown by the arrow in FIG. 11 ) so that the caster assemblies 58 have atrailing orientation with respect to the direction of desired movement.In other words, a start-up force needed to move the patient supportapparatus 30 with the caster assemblies 58 in a non-trailing orientationis much greater than the start-up force needed to move the patientsupport apparatus 30 with the caster assemblies 58 aligned in thetrailing orientation. Often, the orientation that the caster wheels 62assumed when the patient support apparatus 30 was placed in a room isthe opposite orientation that the caster wheels 62 need to assume inorder to move the patient support apparatus 30 out of the room.

To minimize such effort, the controller 68 is configured to control thesteering motor 70 of the caster assembly 58 in response to theorientation of the caster assembly 58 as determined based on the loadsensor 80 readings, as described above. Specifically, the controller 68is configured to control the steering motor 70 to move the casterassembly 58 to the trailing orientation with respect to the direction ofdesired movement. In FIG. 11 , a second state of the caster assembly 58(shown in solid lines) is shown in the trailing position relative to thedesired direction of movement (arrow). The caster assembly 58 is movedto the trailing positon by the steering motor 70 after being rotatedfrom the non-trailing position of the first state.

As such, the techniques described herein provide automatic re-alignmentof the caster assembly 58. Such re-alignment may occur before thepatient support apparatus 30 is manually moved the operator. Forinstance, the operator need not be present near the patient supportapparatus 30 in order for the re-alignment to occur. This is becausere-alignment is based on readings from the load sensor 80 integratedwith the caster assembly 58. Therefore, even while the patient supportapparatus 30 is stationary, the controller 68 can nevertheless make suchdeterminations because the offset caster wheel 62 load is continuouslydetectable by the load sensor 80.

In other examples, the controller 68 may command the steering motor 70to re-align the caster assembly 58 upon detection of movement of thepatient support apparatus 30 in the desired direction of movement.Techniques for determining the desired direction of movement of thepatient support apparatus 30 may be like those described in U.S. PatentApplication Publication No. 2016/0089283, entitled “Patient SupportApparatus,” the disclosure of which is hereby incorporated by referencein its entirety.

Although re-alignment to the trailing position has been described, itshould be appreciated that the controller 68 can command various othertypes of re-alignment of the caster assembly 58 based on readings fromthe load sensor 80. For instance, the controller 68 may command thesteering motor 70 to move the caster wheels 62 to non-trailingorientations for purposes, such as steering of the patient supportapparatus 30 based on prediction of a change in desired direction, orthe like.

It will be further appreciated that the terms “include,” “includes,” and“including” have the same meaning as the terms “comprise,” “comprises,”and “comprising.”

Several embodiments have been discussed in the foregoing description.However, the embodiments discussed herein are not intended to beexhaustive or limit the invention to any particular form. Theterminology which has been used is intended to be in the nature of wordsof description rather than of limitation. Many modifications andvariations are possible in light of the above teachings and theinvention may be practiced otherwise than as specifically described.

What is claimed is:
 1. A patient support apparatus comprising: a base; acaster assembly at least partially supporting the base and including astem, a caster wheel, and a caster wheel axle; a steering motorconfigured to control orientation of the caster assembly; a patientsupport surface coupled to the base and configured to receive asubstantially vertically applied load; a load sensor to measure the loadin a substantially vertical direction; and a controller configured to:control the steering motor based on analyzing measurements of the loadsensor, determine an orientation of the caster assembly based on themeasurements of the load sensor in the substantially vertical direction,and control the steering motor based on the determined orientation. 2.The patient support apparatus of claim 1, wherein the load sensor iscoupled to the stem and is configured to measure load applied to thestem.
 3. The patient support apparatus of claim 2, wherein the loadsensor is a load cell disposed around the stem.
 4. The patient supportapparatus of claim 2, wherein the load sensor is disposed on a distalend of the stem.
 5. The patient support apparatus of claim 4, whereinthe load sensor is a load cell configured to measure compressional forceapplied to the distal end of the stem.
 6. The patient support apparatusof claim 4, wherein the load sensor is a displacement sensor configuredto undergo displacement in response to the load applied to the distalend of the stem and to measure the displacement.
 7. The patient supportapparatus of claim 1, wherein the load sensor is coupled to the casterwheel axle and is configured to measure load applied to the caster wheelaxle.
 8. The patient support apparatus of claim 1, wherein the casterwheel comprises pressurized air and wherein the load sensor comprises apressure sensor configured to measure air pressure of the caster wheel.9. The patient support apparatus of claim 1, wherein the load sensor isconfigured to produce measurements indicative of vertical load andnon-vertical load applied to the caster assembly.
 10. The patientsupport apparatus of claim 9, wherein the controller is configured toanalyze the measurements of the load sensor to determine the loadreceived by the patient support surface by negating the non-verticalload.
 11. The patient support apparatus of claim 1, wherein thecontroller is configured to control the steering motor of the casterassembly to move the caster assembly to a trailing orientation withrespect to a direction of desired movement.
 12. The patient supportapparatus of claim 1, wherein the steering motor is coupled to the stem.13. The patient support apparatus of claim 1, wherein the load sensor isat least one of a load cell, a strain gauge, a pressure sensor, adisplacement sensor, a compression sensor, or a weight sensor.
 14. Apatient support apparatus comprising: a base; a caster assembly at leastpartially supporting the base; a steering motor configured to controlorientation of the caster assembly; a patient support surface coupled tothe base and configured to receive a substantially vertically appliedload; a load sensor integrated into the caster assembly and configuredto produce measurements indicative of the load in a substantiallyvertical direction; and a controller configured to: control the steeringmotor based on analyzing the measurements of the load sensor, determinean orientation of the caster assembly based on analyzing themeasurements of the load sensor in the substantially vertical direction,and control the steering motor based on the determined orientation. 15.The patient support apparatus of claim 14, wherein the controller isconfigured to control the steering motor to move the caster assembly toa trailing orientation with respect to a direction of desired movement.16. The patient support apparatus of claim 14, wherein the casterassembly comprises a stem, wherein the steering motor is coupled to thestem, and wherein the load sensor is a load cell.